Question

A 54-year-old woman is brought to the emergency department via ambulance due to sudden-onset difficulty breathing, lightheadedness, and a diffuse rash. Her symptoms began 20 minutes after eating a meal containing shellfish at a local restaurant. En route and upon arrival, she received a total of 2 L of intravenous normal saline and two separate doses of 0.3 mg intramuscular epinephrine, spaced 5 minutes apart. The patient is lethargic but arousable and complains of a "tight throat" and severe nausea. Her medical history is significant for essential hypertension, generalized anxiety disorder, and migraine headaches. Her daily medications include lisinopril, propranolol, and sertraline. Her temperature is 37.0°C (98.6°F), blood pressure is 76/42 mm Hg, pulse is 62/min, and respirations are 26/min. Oxygen saturation is 94% on 4 L/min via nasal cannula. Physical examination reveals diffuse, intensely pruritic erythematous plaques over the trunk and extremities, along with mild facial and lip swelling. Lung auscultation demonstrates diffuse bilateral expiratory wheezing. She is speaking in short phrases without stridor. Which of the following is the most appropriate immediate next step in the stabilization of this patient?